High speed radio communication services are widely available recently with advent of broad band radio communication standards such as high speed packet access (HSPA) and long term evolution (LTE).
In uplink communication of LTE, a radio access method based on frequency-division multiple access (FDMA) is adopted. That is, the radio base station (eNodeB: evolved nodeB) provides the communication device of the user side with a communication band in accordance with the amount of data, which has not been transmitted yet and remains in the communication device of the user side, so that the communication resources are used efficiently. The communication device of the user side is referred to as user equipment (UE).
Specifically, when the UE receives data in its buffer to be transmitted in the uplink, the UE transmits a scheduling request (SR), which requests allocation of grant, through a physical uplink control channel (PUCCH). Here, “grant” indicates frequency, timing, modulation method and the like, which are used for transmission of uplink data. The PUCCH is a communication channel, which is used in the uplink communication for connection control of communication.
Upon receiving the SR from the UE, the radio base station allocates a grant and commands data transmission under the allocated grant through a physical downlink control channel (PDCCH). The PDCCH is a communication channel, which is used in downlink communication for connection control of communication.
The UE transmits a buffer status report (BSR), which indicates the amount of data remaining in the buffer as data waiting for transmission, through a physical uplink shared channel (PUSCH) corresponding to the grant commanded from the radio base station. The PUSCH is a common data channel for transmitting uplink data.
Upon receiving the BSR, the radio base station re-allocates the grant in accordance with the amount of data indicated in the BSR and commands through the PDCCH transmission of the data stored in the buffer by the allocated grant. The UE sequentially transmits the data in the buffer by using the commanded grant.
The UE further activates a retransmission BSR timer (retx-BSR-timer) in response to the transmission of BSR as a trigger. The retransmission BSR timer is a timer for retransmission of BSR by regarding loss of defect of BSR. Without receiving the control data, which indicates the grant, by expiration of the retransmission BSR timer, the UE performs processing of the transmission of SR, reception of grant and retransmission of BSR.
The BSR is transmitted not only when the retransmission BSR timer expires but also when a periodic BSR timer expires as disclosed in JP 2014-138310.
It is a recent trend to provide not only mobile terminals such as smart phones but also automotive vehicles, machine tools, automatic vending machines and the like with radio communication functions (broad band radio communication function), which complies broad band radio communication standards for realizing high speed data communication. This addition of the radio communication function on various articles will improve added value of products and services, enhance after-service and improve operation efficiency.
For example, in a case that a machine tool is provided with a broad band radio communication function, it is possible to readily monitor time, status and position of operation of the machine tool from remote locations. Further, in a case that a vehicle is provided with a broad band radio communication function, it is possible to provide real-time information services such as traffic information and navigation and monitor position, travel state and compartment temperature of the vehicle on a real-time basis from remote locations. As the purpose of using (that is, application) of the radio communication function spreads widely, it is assumed that more and more services requiring real-time property of communication (that is, small communication delay) and application software (simply referred to as applications) for realizing such are assumed to be developed.
However, when the transmitted BSR is lost, the UE does not restart the uplink communication until the retransmission BSR timer expires. Thus a time interval from activation to expiration of the retransmission BSR timer results in the communication delay.
For this reason, the retransmission BSR timer is set preferably to a relatively small value for applications, which require small communication delay. On the other hand, the retransmission BSR timer is set preferably to a relatively large value for applications, which do not require high real-time property, thereby to limit excessive transmission of BSR.
That is, the retransmission BSR timer in one UE is preferably set in correspondence to real-time property required by the application, which uses the radio communication function provided by the UE. The retransmission BSR timer is presently configured to be set to a value (simply referred to as notified set value), which is transmitted from the radio base station.